Patent Application
20120044601
1. Technical Field
The disclosed embodiments relate to electronic devices, and more particularly to an electronic device with a startup protection circuit.
2. Description of Related Art
Generally, an electronic device includes an initialization circuit and a processing unit, and the electronic device is powered by a supply voltage from a power source. The initialization circuit is used for initializing the processing unit, when the processing unit has initialized completely, the processing unit is ready for use.
However, sometimes, the supply voltage may be too low. In this situation, the processing unit may still start up and try to operate in some way. In such situation, the processing unit may malfunction because of trying to operate with low voltage.
Therefore, there is room for improvement in the art.
Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout two views.
Referring to
The startup protection circuit 200 includes an initialization unit 10 and a protection unit 20. The initialization unit 10 is connected to the processing unit 300. The initialization unit 10 generates a first level signal when initially receiving the supply voltage which is larger than or equal to a predetermined voltage. After the first level signal is generated for a predetermined time period, the initialization unit 10 generates a second level signal.
The processing unit 300 is initialized according to the first level signal, during the predetermined time period, the processing unit 300 may execute built-in software programs. After the predetermined time period, the processing unit 300 has initialized completely. Therefore, the processing unit 300 is ready for use according to the second level signal. In this embodiment, the first level signal is a low level voltage signal, and the second level signal is a high level voltage signal.
The protection unit 20 is connected to the processing unit 300. The protection unit 20 generates the first level signal when the supply voltage is smaller than the predetermined voltage, and stops generating the first level signal when the supply voltage is larger than or equal to the predetermined voltage. Therefore, when the supply voltage is smaller than a predetermined voltage, the processing unit 300 cannot receive the second level signal from the initialization unit 10, thus the processing unit 300 cannot be activated and cannot perform error operations.
Referring to
The protection unit 20 includes a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a first transistor Q1 and a second transistor Q2. The second resistor R2 and the third resistor R3 are connected in series between the power source 400 and ground. A base of the first transistor Q1 is connected between the second resistor R2 and the third resistor R3 through the fifth resistor R5, an emitter of the first transistor Q1 is grounded, a collector of the first transistor Q1 is connected to the power source 400 through the fourth resistor R4. The base of the second transistor Q2 is connected to the collector of the first transistor Q1, the emitter of the second transistor Q2 is grounded, the collector of the second transistor Q2 is connected to the initializing pin 302. In this embodiment, the first transistor Q1 and the second transistor Q2 are npn type transistors.
The principle of the electronic device 100 is as follows:
When the electronic device 100 initially receives the supply voltage from the power source 400, the base of the first transistor Q1 is pulled high, and the first transistor Q1 is turned on. The base of the second transistor Q2 is pulled low, and the second transistor Q2 is turned off. The initializing pin 302 receives a low level voltage signal, and is initialized. The supply voltage charges up the first capacitor C1 and the second capacitor C2 through the first resistor R1, the processing unit 300 has initialized completely after a predetermined time period T, T is calculated by the formula: T=R1×(C1+C2). The initializing pin 302 receives a high level voltage signal, and the processing unit 300 is ready for use.
When the supply voltage from the power source 400 is smaller than the predetermined voltage, the base of the first transistor Q1 is pulled low, and the first transistor Q1 is turned off. The base of the second transistor Q2 is pulled high, and the second transistor Q2 is turned on. The initializing pin 302 also receives a low level voltage signal, and is initialized. Because the initializing pin 302 receives the low level voltage signal when the supply voltage is smaller than the predetermined voltage, the processing unit 300 cannot be activated.
Further alternative embodiments will become apparent to those skilled in the art without departing from the spirit and scope of what is claimed. Accordingly, the present invention should be deemed not to be limited to the above detailed description, but rather only by the claims that follow and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201010256601.0 | Aug 2010 | CN | national |
