JPS5996866A - Control circuit for power source - Google Patents

Abstract

PURPOSE:To improve the accuracy and the responsiveness of a control circuit for a power source by employing a control circuit which detects the current of a main transistor switch to operated at a fast responding speed and an overcurrent control circuit which operates by detecting a load current. CONSTITUTION:Two control circuits of a main circuit A3 which detects the current of a main transistor switch TR to operated at a fast responding speed and an overcurrent control circuit A2 which operates by detecting a load current are prepared. A control circuit A3 which operates at the fast responding speed at the transient time, controls a DC/DC converter, and controls the DC/DC converter by the overcurrent control circuit A2 having high accuracy at the normal time.

Description

DETAILED DESCRIPTION OF THE INVENTION la1 Technical Field of the Invention The present invention relates to a DC-DC converter, and particularly to an overcurrent control circuit.

(bl Conventional technology and problems Figure 1 shows an example of the conventional technology. ■ in the figure shows the power supply,
T is the transformer, TR is the main transistor/switch, D
l, R2, DC is a rectifier, L is a choke coil, CI
, C2 is a capacitor, PWM is a pulse control circuit, A
1 is an amplifier for constant voltage control, El is a reference voltage for constant voltage control, A2 is an amplifier for overcurrent control, R2 is a reference voltage for overcurrent control, R1 is a resistor for overcurrent detection, R2 is a load resistor, Pl
1 and PI2 are photocouplers, and N1, N2, and N3 are the first, second, and third windings of the transformer T.

As shown in FIG. 1, conventionally, when performing constant voltage control and overcurrent control, each control input was taken from the output voltage and output current on the secondary side of the transformer T of the DC-DC converter. That is, in the case of constant voltage control, the terminal voltage of the load resistor R2 and the reference voltage E1 for constant voltage control are always compared, or the terminal voltage of the load resistor R2 is
When the voltage between terminals 2 and 2 decreases, the voltage difference is taken out by the constant voltage control amplifier A1, the photocoupler P1 is operated with a voltage proportional to this voltage difference, and this output drives the pulse control circuit PWM. Then, the output voltage is restored by increasing the energization time (during the pulse) of the main transistor SWITCH TR, which intermittents the current, to increase the output voltage. In the case of overcurrent control, take out the terminal voltage of the overcurrent detection resistor R1 through which the load current always flows, and compare this voltage with the overcurrent control reference voltage E2.
If the load current increases, the differential voltage is similarly extracted by the overcurrent control amplifier A2, the photocoupler P2 is operated by a voltage proportional to this differential voltage, and this output is used to control the pulse control circuit PWM. The energizing time of the main transistor switch TR, which drives the main transistor and switches the current on and off (
(during the pulse) to shorten the load current and restore the load current. Since this method takes the input from the quantity to be ultimately controlled, the characteristics of constant voltage control and overcurrent control are good.

However, it does not detect the current value flowing through the main transistor/switch TR, which is most likely to be damaged during a transient event such as a load short circuit, so there is a drawback that the main transistor/switch TR may be damaged. .

In addition, the power supply for driving the constant voltage control amplifier Al and the overcurrent control amplifier A2 must operate accurately even when the output voltage of the DC-DC converter is abnormal, so a separate auxiliary power supply is required (inconvenient). There are also some points. The circuit consisting of the third winding N3, rectifier D3, and capacitor C2 in Fig. 1 is a constant voltage control amplifier A1 and an overcurrent control amplifier A.
This is an auxiliary power source for driving 2.

(C) Purpose of the Invention The purpose of the present invention is to take advantage of the characteristics of conventional constant voltage control and overcurrent control, while at the same time solving the shortcomings of the above control methods, that is, during transients such as load short circuits, the main transistor switch T , H cannot be detected, and provides a highly reliable overcurrent control circuit for a DC-DC converter with good transient characteristics.

Td1 Configuration of the Invention According to the present invention, the above object is to provide a first overcurrent control circuit that controls the pulse by comparing the voltage generated when the output current flows through the overcurrent detection resistor with a reference voltage; a second overcurrent control circuit that controls the pulse at high speed by comparing a voltage drop obtained by detecting the current flowing through the output current adjustment switch means with another reference voltage; In the control system DC-DC converter,
This is achieved by providing a power supply control circuit characterized in that the operating current level of the first overcurrent control circuit is set to a lower value than the operating current level of the second overcurrent control circuit.

(e) Embodiments of the Invention The overcurrent control circuit of the present invention includes a control circuit A3 with a fast response speed obtained by detecting the current of the main transistor switch TR in a DC-DC converter, and a load current detection circuit. Two control circuits are prepared: the conventional overcurrent control circuit A2 obtained by
3 controls the DC-DC converter, and in normal times it is controlled by the highly accurate control circuit A2.

Embodiments of the present invention will be described in detail below with reference to the drawings.

Fig. 2 is a diagram showing an embodiment of the present invention, in which DTC is a current detector that detects the current value flowing through the main transistor/switch TR, A3 is an amplifier for overcurrent control, and E3 is for overcurrent control. The reference voltage D4 is a rectifier, and the other symbols are the same as in FIG.

In Figure 2, the current in the primary winding of the transformer T of the DC-DC converter, that is, the main transistor switch TR
The current flowing through is detected by the current detector DTC, the difference between the voltage value proportional to this current and the reference voltage E3 is taken, and the difference is amplified by the overcurrent control amplifier A3, and the pulse control circuit P
WM (same as pulse control circuit PWM shown in Figure 1)
to go into. However, this overcurrent control circuit A3 is a conventional overcurrent control circuit A2 that is installed in the output circuit and is composed of an overcurrent control amplifier A2, an overcurrent control reference voltage E2, and an overcurrent detection resistor R1. It is set to start operation at a current level flowing through the main 1-Run sister switch TR which corresponds to a current level greater than the current level at which it starts operation.

In the current detector DTC, the current flowing through the main transistor/switch TR is rectified and smoothed, but by setting the smoothing capacitor in this smoothing circuit to a small value, the A
This makes the response speed faster than in case 2.

Therefore, the second circuit installed with the overcurrent control circuit A3 according to the present invention
The DC-DC converter shown in the figure is normally controlled by an overcurrent control circuit A2 that operates by detecting the output current, but in an emergency where excessive current flows due to a load short circuit, the current flows to the main transistor switch TR. It is controlled at high speed by the overcurrent control circuit A3, which operates by detecting the current. In this way, the components of the DC-DC converter are protected.

Furthermore, the power supply for the overcurrent control circuit A3 according to the present invention is naturally taken from the primary stirring wire side of the transformer T, but when an excessive current that requires the overcurrent control circuit A3 to operate is flowing, the conventional Since the overcurrent control circuit A2 and the constant voltage control circuit etc. do not need to operate normally, there is no need to take their drive power from the tertiary winding side of the transformer T as in the conventional case, as shown by the dotted line in Fig. 2. There is also the advantage that it can be easily obtained from the output voltage as shown in FIG.

In addition, in conventional circuits, when constant voltage control and overcurrent control are used together, constant voltage control is performed using constant voltage control amplifier A1 as shown in Figure 1.
The overcurrent control is performed by the overcurrent control amplifier A2, and the respective output signals are sent to the photocouplers PII and P.
In the present invention, an overcurrent control circuit A3 is installed which operates by detecting the current flowing through the main transistor/switch TR, as shown in Fig. 2. Constant voltage control amplifier A
Even if the output signal of the overcurrent control amplifier A2 and the output signal of the overcurrent control amplifier A2 are collected into the photocoupler P1 by the rectifiers D3 and R4 and sent to the pulse control circuit PWM, the reliability does not decrease.

FIG. 3 is an output static characteristic diagram for explaining the operation status of the two overcurrent control circuits A3 and A2 in the present invention, where the horizontal axis is the output current and the vertical axis is the output voltage. A3 and A2 indicated by arrows in the figure are overcurrent control circuits A3 and A2, respectively.
This represents the result of operation 2.

(f1 Effects of the Invention As explained in detail above, according to the present invention, the advantages of the conventional constant voltage control and overcurrent control characteristics can be utilized, and at the same time, the disadvantages of the above control, namely, the main Improved the point that the current value flowing through the transistor switch TR cannot be detected, resulting in good transient characteristics and high reliability.
This has the advantage that an overcurrent control circuit for a C-DC converter can be provided.

[Brief explanation of the drawing]

FIG. 1 shows a conventional embodiment, where V is a power supply;
T is the transformer, TR is the main transistor/switch, D
I, R2, R3 are rectifiers, L is choke coil, cl
, c2 is a capacitor, PWM is a pulse control circuit, A
1 is an amplifier for constant voltage control, El is a reference voltage for constant voltage control, A2 is an amplifier for overcurrent control, R2 is a reference voltage for overcurrent control, R1 is a resistor for overcurrent detection, R2 is a load resistor, Pl
1 and PI2 are photocouplers, and N1, N2, and N3 are the first, second, and third wires of the transformer T. Figure '2 is a diagram showing an embodiment of the present invention, in which DTC is a current detector that detects the current value flowing through the main transistor switch TR, A3 is an amplifier for overcurrent control, and R3 is for overcurrent control. The reference voltage for R4"i4 and the rectifier, and other symbols are the same as in Fig. 1. Fig. 3 explains the operating situation of the two overcurrent control circuits A3 and A2 in the present invention. This is a diagram for

Claims (1)

[Claims] a first overcurrent control circuit that controls the pulse by comparing the voltage generated when the output current flows through the overcurrent detection resistor with a reference voltage; and a first overcurrent control circuit that detects the current flowing through the output current adjustment switch means. and a second overcurrent control circuit that controls the pulse 1 at high speed by comparing the voltage drop obtained by the voltage drop with another reference voltage.
C converter, a power supply control circuit characterized in that the operating current level of the first overcurrent control circuit is set to a lower value than the operating current level of the second overcurrent control circuit.