Transistor switch control circuit
A synchronous driving circuit in the arts may cause a short through pheromone when a duty cycle of a duty cycle control signal is too short. The present invention sets a delay time with a suitable period when the duty cycle of the duty cycle control signal is too short to avoid the short through phenomenon.
1. A transistor switch control circuit, for controlling a high-side transistor and a low-side transistor connected in series, and the transistor switch control circuit comprising:
a high-side driving circuit, generating a high-side control signal according to a duty cycle control signal to turn on the high-side transistor and generate a high-side conducting signal; and
a low-side driving circuit, generating a low-side control signal according to the duty cycle control signal and the high-side conducting signal to turn on the low-side transistor, and the low-side driving circuit comprising:
a delay circuit, generating a delay signal according to the duty cycle control signal, wherein a pulse width of the delay signal is greater than a pulse width of the duty cycle control signal for more than a predetermined time period; and
a short through preventing circuit, generating the low-side control signal according to the delay signal and the high-side conducting signal, so that the low-side transistor is turned on after the high-side transistor is turned off, and is turned off before the high-side transistor is turned on.
2. The transistor switch control circuit as claimed in claim 1 , wherein the delay circuit adjusts a pulse width difference between the pulse width of the delay signal and the pulse width of the duty cycle control signal according to the pulse width of the duty cycle control signal, so that the wider the pulse width of the duty cycle control signal is, the smaller the pulse width difference is.
3. The transistor switch control circuit as claimed in claim 2 , wherein the delay circuit comprises a controlled current source and a delay capacitor, the controlled current source provides a current to adjust a potential of the delay capacitor according to the pulse width of the duty cycle control signal, and the delay circuit adjusts the pulse width of the delay signal according to the potential of the delay capacitor.
4. The transistor switch control circuit as claimed in claim 3 , wherein the delay circuit further comprises a pulse width determination circuit comprising a current source and a pulse width determination capacitor, wherein the current source charges the pulse width determination capacitor according to the duty cycle control signal.
5. The transistor switch control circuit as claimed in claim 1 , wherein the delay circuit comprises a controlled current source and a delay capacitor, the controlled current source provides a current to adjust a potential of the delay capacitor according to the pulse width of the duty cycle control signal, and the delay circuit adjusts the pulse width of the delay signal according to the potential of the delay capacitor.
6. The transistor switch control circuit as claimed in claim 5 , wherein the delay circuit further comprises a pulse width determination circuit comprising a current source and a pulse width determination capacitor, wherein the current source charges the pulse width determination capacitor according to the duty cycle control signal.
7. A transistor switch control circuit, for controlling a high-side transistor and a low-side transistor connected in series, and the transistor switch control circuit comprising:
a high-side driving circuit, generating a high-side control signal according to a duty cycle control signal to turn on the high-side transistor and generate a high-side conducting signal; and
a low-side driving circuit, generating a low-side control signal according to the duty cycle control signal and the high-side conducting signal to turn on the low-side transistor, and the low-side driving circuit comprising:
a delay circuit, generating a delay signal, wherein a start time point of the delay signal is determined according to a start time point of the duty cycle control signal, and an end time point of the delay signal is determined according to a logic level of the duty cycle control signal after receiving the high-side conducting signal; and
a short through preventing circuit, generating the low-side control signal according to the delay signal and the high-side conducting signal, so that the low-side transistor is turned on after the high-side transistor is turned off, and is turned off before the high-side transistor is turned on.
8. The transistor switch control circuit as claimed in claim 7 , wherein the start time point of the delay signal is a time point when the delay signal is transited from a high level to a low level, and the end time point of the delay signal is a time point when the delay signal is transited from the low level to the high level.
9. The transistor switch control circuit as claimed in claim 7 , wherein the delay circuit starts to determine a logic level of the duty cycle control signal after detecting a rising edge of the high-side conducting signal, and adjusts a logic level of the delay signal according to the logic level of the duty cycle control signal.
10. The transistor switch control circuit as claimed in claim 9 , wherein the delay circuit stops changing the logic level of the delay signal after detecting a rising edge of the duty cycle control signal.
11. The transistor switch control circuit as claimed in claim 8 , wherein the delay circuit starts to determine a logic level of the duty cycle control signal after detecting a rising edge of the high-side conducting signal, and adjusts a logic level of the delay signal according to the logic level of the duty cycle control signal.
12. The transistor switch control circuit as claimed in claim 11 , wherein the delay circuit stops changing the logic level of the delay signal after detecting a rising edge of the duty cycle control signal.