There is an ever-growing proliferation of small appliances that operate as nodes on the IoT or on a standalone basis. Their needs for steady or infrequent power are met by the AP3917 family of non-isolated buck converters.
The new family of buck converters will work with AC inputs ranging from 85 VAC and 265 VAC and provide an 8.0 VDC output.
The AP3917. Image from Diodes Incorporated
The small form factor devices are especially suited for use in applications such as:
- Industrial controls
- Standby and auxiliary
- IoT endpoints
- Non-isolated home appliances, including:
- AC fans
- Rice cookers
- Milk machines
All members of the AP3917 family draw less than 30 mW in standby state. This makes the devices a sure bet for applications that always stay connected, but may nonetheless remain inactive for long periods of time.
Functional block diagram for members of the AP3917 family. Image from Diodes Incorporated
There are currently three family members, with the nominal load being a key variation cited by the company:
The AP3917 buck switchers include multiple protection features for enhanced the system reliability and safety. These include protections against over temperature, output short and overload as well as open loop protection. There is also an under-voltage lock function.
All members of the AP3917 share the following characteristics:
- Improved constant voltage: ±5%
- No load power consumption: < 30mW with external bias
- Frequency modulation to suppress EMI
- They are a low audible noise solution
- Operating temperature range of -40°C to +125°C
Maximal Peak Current
- AP3917B: 280 mA typical
- AP3917C: 420 mA typical
- AP3917D: 500 mA typical
Internal Power MOSFET
- AP3917B: 650 V
- AP3917C: 700 V
- AP3917D: 750 V
The unit is fed through a bridge rectifier and a filter, and surprisingly few other external components. Thus, a clear advantage offered by members of this family is that because so much functionality is incorporated within the converter, fewer external components will be required. The result is a smaller bill of materials, less device real estate taken up, easier manufacturing and a more reliable OEM end product.
A typical application circuit. Image (modified) from Diodes Incorporated
Peak current and switching frequency for AP3917 devices reduce as the load decreases. This makes for excellent efficiency performance at light loads and improves the overall system efficiency.
All members of the AP3917 family are available in a SO-7 package.
Around the Industry
Today, situations abound where there is ample high voltage power available, but a device only needs a small amount of low voltage power, often on an intermittent basis.
Many manufacturers are harkening to fill that need. Engineers should keep in mind that most, like the members of the AP3917 family, do not include the bridge rectifier or inductor internally. Here’s one example.
STMicroelectronics offers a high-voltage converter, the VIPer26K from STMicroelectronics. This device can be utilized to implement low-power, switched-mode AC to DC power supplies up to a maximum power of 15 watts.