输出的脉宽调制集液晶/LED驱动器
abstract: the digital, pulse-width-modulation (pwm) output available from many microprocessors is based on an internal 8- or 16-bit counter and features a programmable duty cycle. it is suitable for adjusting the output of an lcd driver, a negative-voltage led driver, or a current-controlled led driver.
the digital, pulse-width-modulation (pwm) output available from many microprocessors is based on an internal 8- or 16-bit counter and features a programmable duty cycle. it is suitable for adjusting the output of an lcd driver (figure 1), a negative-voltage led driver (figure 2), or a current-controlled led driver (figure 3).
figure 1. lcd driver with positive output voltage.
figure 2. lcd driver with negative output voltage.
figure 3. current-controlled led driver.
the circuit consists simply of a pwm source, capacitor c, and resistors rd and rw. for cmos outputs, you calculate the open-circuit output voltage as:
where d is the pwm duty cycle and vdd is the logic supply voltage. the control circuit's output impedance is the sum of resistor values rw and rd:
for the circuit of figure 1, the output voltage (vout) is a function of the pwm average voltage (vcont):
where vref is the reference voltage at the feedback input.
bear in mind that the initial charge on filter capacitor c produces a turn-on transient. the capacitor forms a time constant with rcont, which causes the output to initialize at a voltage higher than that intended. you can minimize this overshoot by scaling the value of rd as high as possible with respect to r1 and r2. as an alternative, the µp can disable the lcd until the pwm voltage stabilizes.
for figure 2, the output voltage (vout) is a function of the pwm average voltage (vcont):
where vref is the reference voltage at the feedback input.
for figure 3, the output current (iout) is a function of the pwm average voltage (vcont):
where vref is the reference voltage at the set output and k is the current-scaling factor.
rd isolates the capacitor from the feedback loop in these pwm-adjustment methods. assuming a stable voltage at the feedback point, the following equation defines the lowpass filter's cutoff frequency:
where r = rw rd. if rd >> rw, r ≈ rw. to minimize ripple voltage at the output, you should set the cutoff frequency at least two decades below the pwm frequency.
高速图像压缩芯片“雅芯-天图”成功应用
大彩M系列精简核心板结构串口屏发布，提供IO/USB扩展口二次开发
2021第八届海峡两岸（南京）新型显示产业高峰论坛成功举办
共筑开源安全 | 软通动力作为发起单位加入“开放原子开源基金会开源安全委员会”
简要介绍了操作系统虚拟化的概念，以及实现操作系统虚拟化的技术
输出的脉宽调制集液晶/LED驱动器
LPC21o4处理器结构及特性介绍
我们正在进入一个数据存储的新时代
盘点机器学习推动运输与物流行业变革的几种方式
5G芯片质量控制、测试提高芯片安全……OFweek第二期工程师技术专场演讲回顾！
TI新推出QFN封装蓝牙无线连结系列产品
华为荣耀V9怎么样？荣耀V9、华为P10和P10Plus大PK，看看谁能笑到最后！
ARM发力物联网 收购两家公司
基于Zynq的嵌入式系统教学改革背景与措施
PFC控制器CS1501的主要特性及典型应用电路
图像采集卡的工作原理
MIMO和分布式天线系统(DAS)技术简述
iPad 2初期销量或高于一代
射频PCB布局中的波导腔设计
区块链是一条失信的不归路吗
the digital, pulse-width-modulation (pwm) output available from many microprocessors is based on an internal 8- or 16-bit counter and features a programmable duty cycle. it is suitable for adjusting the output of an lcd driver (figure 1), a negative-voltage led driver (figure 2), or a current-controlled led driver (figure 3).
figure 1. lcd driver with positive output voltage.
figure 2. lcd driver with negative output voltage.
figure 3. current-controlled led driver.
the circuit consists simply of a pwm source, capacitor c, and resistors rd and rw. for cmos outputs, you calculate the open-circuit output voltage as:
where d is the pwm duty cycle and vdd is the logic supply voltage. the control circuit's output impedance is the sum of resistor values rw and rd:
for the circuit of figure 1, the output voltage (vout) is a function of the pwm average voltage (vcont):
where vref is the reference voltage at the feedback input.
bear in mind that the initial charge on filter capacitor c produces a turn-on transient. the capacitor forms a time constant with rcont, which causes the output to initialize at a voltage higher than that intended. you can minimize this overshoot by scaling the value of rd as high as possible with respect to r1 and r2. as an alternative, the µp can disable the lcd until the pwm voltage stabilizes.
for figure 2, the output voltage (vout) is a function of the pwm average voltage (vcont):
where vref is the reference voltage at the feedback input.
for figure 3, the output current (iout) is a function of the pwm average voltage (vcont):
where vref is the reference voltage at the set output and k is the current-scaling factor.
rd isolates the capacitor from the feedback loop in these pwm-adjustment methods. assuming a stable voltage at the feedback point, the following equation defines the lowpass filter's cutoff frequency:
where r = rw rd. if rd >> rw, r ≈ rw. to minimize ripple voltage at the output, you should set the cutoff frequency at least two decades below the pwm frequency.
高速图像压缩芯片“雅芯-天图”成功应用
大彩M系列精简核心板结构串口屏发布，提供IO/USB扩展口二次开发
2021第八届海峡两岸（南京）新型显示产业高峰论坛成功举办
共筑开源安全 | 软通动力作为发起单位加入“开放原子开源基金会开源安全委员会”
简要介绍了操作系统虚拟化的概念，以及实现操作系统虚拟化的技术
输出的脉宽调制集液晶/LED驱动器
LPC21o4处理器结构及特性介绍
我们正在进入一个数据存储的新时代
盘点机器学习推动运输与物流行业变革的几种方式
5G芯片质量控制、测试提高芯片安全……OFweek第二期工程师技术专场演讲回顾！
TI新推出QFN封装蓝牙无线连结系列产品
华为荣耀V9怎么样？荣耀V9、华为P10和P10Plus大PK，看看谁能笑到最后！
ARM发力物联网 收购两家公司
基于Zynq的嵌入式系统教学改革背景与措施
PFC控制器CS1501的主要特性及典型应用电路
图像采集卡的工作原理
MIMO和分布式天线系统(DAS)技术简述
iPad 2初期销量或高于一代
射频PCB布局中的波导腔设计
区块链是一条失信的不归路吗