ISOLATED DC-DC CONVERTER

• US 20100246215A1
• Filed: 03/23/2010
• Published: 09/30/2010
• Est. Priority Date: 03/25/2009
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toyota Jidoshokki
• Original Assignee: Kabushiki Kaisha Toyota Jidoshokki
• Inventors: OYABU, Toyohisa, HIRABAYASHI, Nobuo, MASE, Tomoyuki
• Granted Patent: US 8,670,247 B2
• Time in Patent Office: Days
• US Class Current: 363/21.40
• CPC Class Codes: H02M 1/36 Means for starting or stopping converters
• CPC Class Codes: H02M 1/40 Means for preventing magnetic saturation
• CPC Class Codes: H02M 3/33569 having several active switching elements H02M3/3353 takes precedence
• CPC Class Codes: H02M 3/33571 Half-bridge at primary side of an isolation transformer

Abstract

An isolated DC-DC converter includes a transformer, a main switch, an active clamp circuit and a control unit. The transformer has a primary winding. The main switch and the active clamp circuit are connected to the primary winding. The active clamp circuit has an auxiliary switch and a clamp capacitor connected in series. The control unit is provided for controlling the main switch and the auxiliary switch. The control unit performs a soft start operation of the converter before a normal operation. The control unit performs anti-saturation control before starting the soft start operation. The anti-saturation control includes an act of controlling the main switch and the auxiliary switch so that the auxiliary switch performs ON-OFF operation with the main switch kept OFF until voltage of the clamp capacitor drops below a level at which the transformer is to be magnetically saturated after starting the soft start operation.

Claims

1. An isolated DC-DC converter comprising:

a transformer having a primary winding;

a main switch connected to the primary winding;

an active clamp circuit connected to the primary winding, wherein the active clamp circuit has an auxiliary switch and a clamp capacitor being connected in series; and

a control unit for controlling the main switch and the auxiliary switch, wherein the control unit performs a soft start operation of the isolated DC-DC converter before a normal operation for supplying power, wherein the control unit performs anti-saturation control before starting the soft start operation of the isolated DC-DC converter, wherein the anti-saturation control includes an act of controlling the main switch and the auxiliary switch so that the auxiliary switch performs ON-OFF operation while the main switch is kept in OFF state until voltage of the clamp capacitor drops below a level at which the transformer is to be magnetically saturated after starting the soft start operation of the isolated DC-DC converter.

2. The isolated DC-DC converter according to claim 1, wherein the control unit performs the anti-saturation control before restarting the soft start operation of the isolated DC-DC converter after a stop of the isolated DC-DC converter.

3. The isolated DC-DC converter according to claim 1, wherein a time period of the auxiliary switch being ON in the anti-saturation control is set so that product of remaining charge of the clamp capacitor and the time period of the auxiliary switch being ON is smaller than volt-time product E·

T in which a voltage E across the transformer is multiplied by a time period T while the voltage E is applied to the transformer.

4. The isolated DC-DC converter according to claim 1, wherein a cycle of the ON-OFF operation of the auxiliary switch in the anti-saturation control is equal to a cycle of the ON-OFF operation of the auxiliary switch during the normal operation of the isolated DC-DC converter.

5. The isolated DC-DC converter according to claim 1, wherein the control unit maintains the anti-saturation control until a cumulative pulse number of the auxiliary switch from initiation of the anti-saturation control reaches a preset number of times.

6. The isolated DC-DC converter according to claim 1, wherein the control unit maintains the anti-saturation control until time from initiation of the anti-saturation control reaches a preset time.

7. The isolated DC-DC converter according to claim 1, wherein the control unit maintains the anti-saturation control until the voltage of the clamp capacitor detected by a voltage detecting circuit drops below a preset level.

8. The isolated DC-DC converter according to claim 1, wherein the voltage of the clamp capacitor dropping below the level at which the transformer is to be magnetically saturated is above zero.

9. The isolated DC-DC converter according to claim 1, wherein the isolated DC-DC converter is an active clamp forward converter having a single or two separate transformers.

10. The isolated DC-DC converter according to claim 1, wherein the isolated DC-DC converter is a boost half-bridge converter, wherein the clamp circuit is connected in parallel to either the primary winding or a series circuit of the primary winding and a capacitor.